Miguel Britos scored a stoppage time equaliser to deny Liverpool all three points and a famous comeback thanks to poor defending at a corner.

The hosts took the lead through Stefano Okaka, who was a constant menace for the Reds' back line, heading home, unmarked, from a delightful Jose Holebas corner.

Sadio Mane did his best impression of Thierry Henry to curl in the equaliser, but it didn't last long as Abdoulay Doucoure profited from more abject Liverpool defending to regain the lead.

A quick-fire double from Klopp's side in the second half showed they will live and die by their mouthwatering attack, first through Firmino's penalty after Heurelho Gomes took down Mohamed Salah.

Then then Egyptian tapped home what looked to be the winner after Firmino's lob appeared to be drifting just wide, but Britos stabbed home from close range after Simon Mignolet failed to keep out Richarlison's powerful drive from a tight angle.

Here are five talking points from Vicarage Road.

Amrabat congratulates Okaka (Image: Getty Images Europe)

Mane finished well to equalise (Image: Reuters)

Firmino congratulates Salah on his goal (Image: Getty Images Europe)

Mohamed Salah celebrates his debut goal (Image: Getty Images Europe)

1. Liverpool still can't defend

Jurgen Klopp continues to overlook his side's most glaring issue: they cannot defend and while Virgil van Dijk would help, it's an issue best solved by coaching, which appears to be beyond the German.

Zonal marking at corners can work, but why is Roberto Firmino installed in the most dangerous area? The Brazilian failed to anticipate Stefano Okaka, perhaps Watford's biggest weapon at set-pieces, who powered home the opener from Jose Holebas' beautifully-delivered corner.

More confusion occurred in stoppage time as Richarlison was allowed to drive at goal and nobody picked up Miguel Britos on the goal line who equalised late on.

It's an area that needs addressing urgently and while help can be acquired in the market, Klopp must dedicate more time to it on the training ground if the Reds are to make top four again.

Okaka rises to head in the opener (Image: Liverpool FC)

The Italian powers home the opener (Image: PA)

2. Mane to emerge as Reds' primary source of goals

Sadio Mane will be a real force this season if he can remain fit for the entire campaign.

The Senegalese has express pace and no desire to take the long route to goal, which proved so effective in the equaliser.

Sharp and intelligent on the ball, Mane's pace hurts you over five meters by reacting quickest in search of the return ball and his finishing is underrated too.

Emre Can challenges Chalobah (Image: Getty Images Europe)

Romelu Lukaku and Harry Kane may prove too prolific, but Mane, even from a wide berth, can emerge as a prolific goalscorer and reach 20 goals after a decent return of 13 in his debut season.

Mane curls home the equaliser (Image: REUTERS)

The Senegalese star celebrates his goal (Image: REUTERS)

3. Chalobah has bright season ahead

Nathaniel Chalobah resisted staying for another season with Chelsea in favour of first team football under Marco Silva.

The England under-21 international kept it nice and tidy and looks to have found a promising partner to anchor the Hornets' midfield with Abdoulay Doucoure.

Liverpool's trio were matched for large spells and with Gareth Southgate a known admirer and Silva set to integrate more attacking quality in the weeks ahead—Troy Deeney, Andre Gray and Richarlison—Chalobah can prosper in yellow and prove himself as a candidate for next year's World Cup squad.

4. Pre-season means nothing and Moreno's time is up

Alberto Moreno has enjoyed a fine pre-season, catching the eye and leading many to believe he can salvage his Liverpool career.

Jamie Carragher was adamant he did not deserve the lifeline based on pre-season alone: "I must say I don't like the fact that Klopp is judging him on pre-season, a couple of good games, it's not the place.

"I don't like the fact he's giving him the chance on the back of pre-season, he knows the players, he's had him for 18 months."

Moreno was weak in the challenge deep inside in his own half, which allowed Abdoulaye Doucouré to complete the turnover and send it wide to Tom Cleverly, whose cross led to the French midfielder dispatching the loose ball for the home side's second.

Moreno struggled throughout (Image: Action Images via Reuters)

Mane is challenged by Janmaat (Image: Action Images via Reuters)

5. Okaka can be a surprise weapon for Silva

Stefano Okaka appeared to be starting due to circumstances, with Troy Deeney injured and Andre Gray having only signed a few days ago.

But the Italian is a real handful and could remain a regular part of this Watford side, bringing out the best in Gray and reducing his work load.

One of the strongest forwards in the league, Okaka offers an aerial threat and can help link the play beautifully with his back to goal. If he can provide 10 goals, Silva will certainly be content to persevere with him in the side.